A silicon wafer is the material on which integrated circuit (IC) chips are made. The manufacturing of IC chips requires a very high-vacuum environment. A suitable high-vacuum environment may be created with a properly designed and manufactured vacuum system. Vacuum systems for the manufacturing of IC chips on silicon wafers are generally known. There are many associated parts to a vacuum system, but it can generally be described as having two main sections: the pump and the chamber. These two sections are generally divided by a gate valve, which seals the two sections off from each other.
After assembling a vacuum system, the vacuum system is tested at a high vacuum setpoint pressure at least as high as the vacuum that it will be expected to achieve when actually manufacturing IC chips on silicon wafers. The vacuum test essentially qualifies the system to be operated at pressures up to the high vacuum setpoint pressure. This test may take up to several hours or days to perform, because the first time that a new system is subjected to a high vacuum, various types of impurities and contaminants may be in the system, having been introduced into the parts of the assembly during its manufacture. The impurities and contaminants will desorb from the surfaces of the interior of the system when subjected to a vacuum. A greater contamination will cause a faster desorption rate of gases from the interior surfaces into the interior space, and a faster introduction of gases into the interior space results in a longer time to achieve the setpoint pressure. A vacuum system may become recontaminated after the first vacuum period, but typically not to the extent of contamination prior to the first vacuum period, so the vacuum test typically takes longer to achieve the setpoint pressure than do subsequent vacuum periods. The bakeout period is the time that the system is subjected to a high vacuum, during which the impurities and contaminants are desorbed and removed from the interior of the system, prior to determining the setpoint pressure. The vacuum test ends when the vacuum of the system reaches the desired vacuum setpoint pressure and is able to maintain it after the expected time for the test has elapsed.
If the vacuum system fails the test, then it will have to be fixed, or the system will have to be scrapped. These vacuum systems can be very expensive, making it very undesirable to have to scrap an entire system. Therefore, the manufacturer of the system will usually try to troubleshoot the problem in order to save the system. Troubleshooting involves diagnosing the problem and repairing it.
The base pressure of a vacuum system is the lowest pressure down to which the system can be pumped. If the base pressure can reach or exceed the qualifying base pressure, the setpoint pressure, e.g. 6.0.times.10.sup.-9 torr, then the vacuum system has passed the vacuum test. The base pressure is determined by measuring the pressure after bakeout while the pump holds the system steady at the ultra high vacuum. If the base pressure has not reached the qualifying base pressure, then the vacuum system has failed the base pressure test, and troubleshooting may be required.
The rate of rise (ROR) of a vacuum system is the rate at which the pressure inside the chamber rises after the chamber has been isolated from the pump by closing the gate valve. The ROR is measured by closing off the gate valve and measuring the pressure over a period of time, e.g. 2 minutes. If the pressure rises slowly enough, e.g. at a qualifying ROR of 1.5.times.10.sup.-6 torr/2 min or less, then the vacuum system has passed the ROR vacuum test. If the pressure rises faster than the qualifying ROR, then the vacuum system has failed, and additional troubleshooting may be required.
Troubleshooting involves determining the cause of the base pressure and/or ROR failure. Problems arise when the nature of the cause is not readily apparent. An operator may replace various components of the vacuum system and then retest the system, but without a clear indication of the nature of the cause of the failure, the operator is left uncertain over which parts to replace. Indiscriminate or random replacement of components and retesting can be both time-consuming and costly.
It is, therefore, desirable to have a method of diagnosing a vacuum system that has a failed base pressure or ROR, that quickly identifies the most likely cause of the failure.